Katakana is also a syllabary, and it is used to write foreign words, loanwords, and onomatopoeia. There are 46 katakana characters, and they are similar in shape to hiragana characters, but they have different pronunciations.
Kanji is a system of writing that uses Chinese characters. There are thousands of kanji characters, and they can each have multiple meanings and pronunciations. Kanji are used to write the majority of words in Japanese.